Fuel vapor purging diagnostics

ABSTRACT

Systems and methods are provided for monitoring reverse flow of fuel vapors and/or air through a vehicle fuel vapor recovery system, the fuel vapor recovery system coupled to an engine intake of a boosted internal combustion engine. One example method comprises, intermittently adjusting a restriction in the fuel vapor recovery system during boosted conditions, and indicating degradation based on one or more of a change in a pressure value, or based on a change in flow in the fuel vapor recovery system.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/399,213 filed Mar. 6, 2009, the entire contents of which areincorporated herein by reference for all purposes.

FIELD

The present description relates to methods and systems for monitoringflow and diagnosing flow errors in a fuel vapor recovery system for avehicle with a boosted internal combustion engine.

BACKGROUND/SUMMARY

Vehicles may be fitted with evaporative emission control systems such asonboard refueling vapor recovery (ORVR) systems. Such systems captureand reduce release of vaporized hydrocarbons to the atmosphere, forexample fuel vapors released from a vehicle gasoline tank duringrefueling. Specifically, the vaporized hydrocarbons (HCs) are stored ina fuel vapor canister packed with an adsorbent which adsorbs and storesthe vapors. At a later time, when the engine is in operation, theevaporative emission control system allows the vapors to be purged intothe engine intake manifold for use as fuel.

Various approaches have been developed for detecting fuel vapor leaks insuch ORVR systems. However, the inventors have recognized severalpotential issues with such methods. The inventors have recognized thatit is possible for a reverse flow of air and/or fuel vapors through theORVR system (for example, from the intake manifold to the fuel tank) tooccur. Specifically, such reverse flows may occur in the case where acanister check valve is stuck open and/or a canister purge valve isstuck open. Likewise, it is also possible for the canister purge valveand/or check valve to degrade in boosted engines wherein the intakemanifold pressure (MAP) is substantially above atmospheric pressurelevels. Consequently, the purge flow may overcome a pressure reliefvalve (such as a pressure relief valve in the fuel tank cap), causingthe fuel tank and the fuel vapor canister to over-inflate and exceeddesign limits of pressure. Furthermore, the reverse flow of fuel vaporsthrough the canister purge system may cause hydrocarbon vapors to escapeinto the atmosphere and degrade emissions quality.

Thus, in one example, some of the above issues may be addressed by amethod of monitoring reverse flow of fuel vapors and/or air through avehicle fuel vapor recovery system, said fuel vapor recovery systemcoupled to an engine intake of a boosted internal combustion engine. Inone example, the method comprises, intermittently adjusting arestriction in the fuel vapor recovery system during boosted conditions,and indicating degradation based on one or more of a change in apressure value, or based on a change in flow in the fuel vapor recoverysystem.

In this way, by sensing changes in fluid pressure and/or fluid flow in afuel vapor recovery system, for example fluid pressure and/or fluid flowchanges across a component of the fuel vapor recovery system (such as afuel tank pressure sensor), improper flow through a fuel vapor recoverysystem coupled to a boosted engine system may be identified. Byidentifying improper flow of air through the fuel vapor recovery system,for example, reverse flow of boosted air from an engine intake manifold,degradation of the fuel vapor recovery system may be reduced. Bypromptly disabling boost responsive to the reverse flow, damage to fuelvapor system components, such as valves, canisters, and/or fuel tanks,may be reduced. Additionally, reverse flow induced excessive evaporativeemissions may also be addressed.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an engine and an associated fuelvapor recovery system.

FIGS. 2-6, and 17 show alternate embodiments of the fuel vapor recoverysystem of FIG. 1.

FIGS. 7-12 show high level flow charts illustrating pressure-sensitiveroutines that may be implemented for identifying reverse flow andrelated component degradation in the fuel vapor recovery system of FIG.1.

FIG. 13 shows a map depicting changes in manifold pressure responsive tochanges in the state of a canister vent valve, as may be used foridentifying reverse flow in the routine of FIG. 9.

FIG. 14 shows a map depicting changes in fuel tank pressure responsiveto changes in the state of a canister vent solenoid, as may be used foridentifying component degradation in the routine of FIG. 10.

FIGS. 15-16 show high level flow charts illustrating flow-sensitiveroutines that may be implemented for identifying reverse flow andrelated component degradation in the fuel vapor recovery system of FIG.1.

DETAILED DESCRIPTION

The following description relates to systems and methods for monitoringair flow and pressure changes in the fuel vapor recovery system of avehicle with a boosted combustion engine, such as depicted in FIG. 1, tothereby reduce over-pressure related component degradation. As shown inFIGS. 2-6 and 17, a fuel tank pressure transducer may be configured todetect improper flow of air and/or fuel vapors through the fuel vaporrecovery system, while complementing its role in engine-off naturalvacuum leak detection. As such, if left undetected, such reverse flowsmay lead to system component over-pressure, component degradation,and/or excessive evaporative emissions. An engine controller may beconfigured to perform diagnostic routines, such as those depicted inFIGS. 7-12 and 15-16, to identify reverse flow through the fuel vaporrecovery system and/or further identify the nature of componentdegradation. Such diagnostic routines may identify reverse flow based oncharacteristic changes in a pressure value, such as a fuel tank pressureand/or a manifold air pressure, or based on a change in flow. Byidentifying reverse flow and/or over-pressure related conditions,over-pressure related component degradation in a fuel vapor recoverysystem may be reduced. By enabling fuel vapor recovery and purging toproceed as described herein, degradation of emissions quality due toexcess evaporative release of fuel vapor hydrocarbons can also bereduced.

FIG. 1 shows a schematic depiction of a vehicle system 6. The vehiclesystem 6 includes an engine system 8 coupled to a fuel vapor recoverysystem 22 and a fuel system 18. The engine system 8 may include anengine 10 having a plurality of cylinders 30. The engine 10 includes anengine intake 23 and an engine exhaust 25. The engine intake 23 includesa throttle 62 fluidly coupled to the engine intake manifold 44 via anintake passage 42. The engine exhaust 25 includes an exhaust manifold 48leading to an exhaust passage 35 that routes exhaust gas to theatmosphere. The engine exhaust 25 may include one or more emissioncontrol devices 70, which may be mounted in a close-coupled position inthe exhaust. One or more emission control devices may include athree-way catalyst, lean NOx trap, diesel particulate filter, oxidationcatalyst, etc. It will be appreciated that other components may beincluded in the engine such as a variety of valves and sensors, asfurther elaborated in the example embodiments of FIGS. 2-6.

The engine intake 23 may further include a boosting device, such as acompressor 74. Compressor 74 may be configured to draw in intake air atatmospheric air pressure and boost it to a higher pressure. As such, theboosting device may be a compressor of a turbocharger, where the boostedair is introduced pre-throttle, or the compressor of a supercharger,where the throttle is positioned before the boosting device. Using theboosted intake air, a boosted engine operation may be performed.

Fuel system 18 may include a fuel tank 20 coupled to a fuel pump system21. The fuel pump system 21 may include one or more pumps forpressurizing fuel delivered to the injectors of engine 10, such as theexample injector 66 shown. While only a single injector 66 is shown,additional injectors are provided for each cylinder. It will beappreciated that fuel system 18 may be a return-less fuel system, areturn fuel system, or various other types of fuel system. Vaporsgenerated in fuel system 18 may be routed to a fuel vapor recoverysystem 22, described further below, via conduit 31, before being purgedto the engine intake 23. Conduit 31 may optionally include a fuel tankisolation valve. Among other functions, fuel tank isolation valve mayallow a fuel vapor canister of the fuel vapor recovery system to bemaintained at a low pressure or vacuum without increasing the fuelevaporation rate from the tank (which would otherwise occur if the fueltank pressure were lowered). The fuel tank 20 may hold a plurality offuel blends, including fuel with a range of alcohol concentrations, suchas various gasoline-ethanol blends, including E10, E85, gasoline, etc.,and combinations thereof. A fuel tank pressure transducer (FTPT) 120, orfuel tank pressure sensor, may be included between the fuel tank 20 andfuel vapor recovery system 22, to provide an estimate of a fuel tankpressure, and for engine-off leak detection. The fuel tank pressuretransducer may alternately be located in conduit 31, purge line 28, vent27, or fuel vapor recovery system 22, without affecting its engine-offleak detection ability.

Fuel vapor recovery system 22 may include one or more fuel vaporrecovery devices, such as one or more fuel vapor canisters filled withan appropriate adsorbent, the canisters configured to temporarily trapfuel vapors (including vaporized hydrocarbons) during fuel tankrefilling operations and “running loss” (that is, fuel vaporized duringvehicle operation). In one example, the adsorbent used is activatedcharcoal. Fuel vapor recovery system 22 may further include a vent 27which may route gases out of the recovery system 22 to the atmospherewhen storing, or trapping, fuel vapors from fuel system 18. Vent 27 mayalso allow fresh air to be drawn into fuel vapor recovery system 22 whenpurging stored fuel vapors from fuel system 18 to engine intake 23 viapurge line 28 and purge valve 112. A canister check valve 116 may alsobe included in purge line 28 to prevent (boosted) intake manifoldpressure from flowing gases into the purge line in the reversedirection. While this example shows vent 27 communicating with fresh,unheated air, various modifications may also be used. Flow of air andvapors between fuel vapor recovery system 22 and the atmosphere may beregulated by the operation of a canister vent solenoid (not shown),coupled to canister vent valve 108. A detailed system configuration offuel vapor recovery system 22 is described herein below with regard toFIGS. 2-6, including various additional components that may be includedin the intake, exhaust, and fuel system.

The vehicle system 6 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust gassensor 126 located upstream of the emission control device, temperaturesensor 128, and pressure sensor 129. Other sensors such as pressure,temperature, air/fuel ratio, and composition sensors may be coupled tovarious locations in the vehicle system 6, as discussed in more detailherein. As another example, the actuators may include fuel injector 66,valve 29, and throttle 62. The control system 14 may include acontroller 12. The controller may receive input data from the varioussensors, process the input data, and trigger the actuators in responseto the processed input data based on instruction or code programmedtherein corresponding to one or more routines. Example control routinesare described herein with regard to FIGS. 7-12, and 15-16.

Fuel vapor recovery system 22 operates to store vaporized hydrocarbons(HCs) from fuel system 18. Under some operating conditions, such asduring refueling, fuel vapors present in the fuel tank may be displacedwhen liquid is added to the tank. The displaced air and/or fuel vaporsmay be routed from the fuel tank 20 to the fuel vapor recovery system22, and then to the atmosphere through vent 27. In this way, anincreased amount of vaporized HCs may be stored in fuel vapor recoverysystem 22. During a later engine operation, the stored vapors may bereleased back into the incoming air charge using the intake manifoldvacuum. Specifically, the fuel vapor recovery system 22 may draw freshair through vent 27 and purge stored HCs into the engine intake forcombustion in the engine. Such purging operation may occur duringselected engine operating conditions as described herein.

FIGS. 2-6 depict alternate embodiments of fuel vapor recovery system 22.It will be appreciated that like numbered components introduced in oneembodiment may be referenced similarly in other embodiments and may notbe reintroduced for reasons of brevity.

FIG. 2 shows an example embodiment 200 of fuel vapor recovery system 22.Fuel vapor recovery system 22 may include one or more fuel vaporretaining devices, such as one or more of a fuel vapor canister 202.Canister 202 may be filled with an adsorbent capable of binding largequantities of vaporized HCs. In one example, the adsorbent used isactivated charcoal. Canister 202 may receive fuel vapors from fuel tank20 through conduit 31. While the depicted example shows a singlecanister, it will be appreciated that in alternate embodiments, aplurality of such canisters may be connected together.

A fuel level sensor 206 (also known as a “fuel sender”), located in fueltank 20, may provide an indication of the fuel level (“Fuel LevelInput”) to controller 12. As depicted, fuel level sensor 206 maycomprise a float connected to a variable resistor. Alternatively, othertypes of fuel level sensors may be used. In one example, fuel tank 20may further include an optional pressure relief valve. However, inalternate embodiments, the fuel tank pressure relief valve may befunctionally integrated into the canister vent solenoid so that tankvapors may not be directly vented to the atmosphere with passing overthe adsorbant.

Further, a tank isolation valve 205 may optionally be placed in conduit31 to temporarily prevent fuel vapor pressure from transmitting itselfto the rest of fuel vapor control system. In one example, the tankisolation valve may be mounted on the fuel tank. In another example, asdepicted herein, the tank isolation valve may be coupled to the fueltank along conduit 31. As such, optional tank isolation valve 205 mayprevent vapor flow to fuel vapor canister 202, thereby reducingevaporation of fuel in the tank. Thus, in the absence of tank isolationvalve 205, fuel tank 20 may be exposed to low intake manifold pressuresthat can accelerate vapor generation. Additionally, canister purging maybe most effective with the tank isolated from the canister.

Fuel vapor recovery system 22 may communicate with the atmospherethrough vent 27. Canister vent valve 108 may be located along vent 27,coupled between the fuel vapor canister and the atmosphere, and mayadjust flow of air and vapors between fuel vapor recovery system 22 andthe atmosphere. Operation of the canister vent valve 108 may beregulated by a canister vent solenoid (not shown). Based on whether thefuel vapor recovery system is to be sealed or not sealed from theatmosphere, the canister vent valve may be closed or opened.Specifically, controller 12 may energize the canister vent solenoid toclose canister vent valve 108 and seal the system from the atmosphere.In contrast, when the canister vent solenoid is at rest, the canistervent valve 108 may be opened and the system may be open to theatmosphere. Further still, controller 12 may be configured to adjust theduty cycle of the canister vent solenoid to thereby adjust the pressureat which the canister vent valve is relieved. In one example, during afuel vapor storing operation (for example, during a fuel tank refillingand while the engine is not running), the canister vent solenoid may bede-energized and the canister vent valve may be opened so that air,stripped of fuel vapor after having passed through the canister, can bepushed out to the atmosphere. In another example, during a purgingoperation (for example, during a canister regeneration and while theengine is running), the canister vent solenoid may be de-energized andthe canister vent valve may be opened to allow a flow of fresh air tostrip the stored vapors of the activated charcoal.

As further elaborated in FIGS. 8-9, the controller may command thecanister vent valve to be intermittently closed, by adjusting operationof the canister vent solenoid, to diagnose reverse flow through the fuelvapor recovery system. By commanding the canister vent valve to beclosed, the controller may seal the fuel vapor recovery system from theatmosphere.

Fuel vapors released from canister 202, for example during a purgingoperation, may be directed into intake manifold 44 via purge line 28.The flow of vapors along purge line 28 may be regulated by canisterpurge valve 112, coupled between the fuel vapor canister and the engineintake. As depicted, canister purge valve 112 may be a ball check valve,although alternative check valves may also be used. The quantity andrate of vapors released by the canister purge valve may be determined bythe duty cycle of an associated canister purge valve solenoid 214. Assuch, the duty cycle of the canister purge valve solenoid may bedetermined by the vehicle's powertrain control module (PCM), such ascontroller 12, responsive to engine operating conditions, including, forexample, an air-fuel ratio. By commanding the canister purge valve to beclosed, the controller may seal the fuel vapor recovery system from theengine intake.

An optional canister check valve 116 may also be included in purge line28 to prevent intake manifold pressure from flowing gases in theopposite direction of the purge flow. As such, the check valve may benecessary if the canister purge valve control is not accurately timed orthe canister purge valve itself can be forced open by a high intakemanifold pressure. An estimate of the manifold absolute pressure (MAP)may be obtained from MAP sensor 218 coupled to intake manifold 44, andcommunicated with controller 12. Alternatively, MAP may be inferred fromalternate engine operating conditions, such as a manifold air flow(MAF), as measured by a MAF sensor (not shown) coupled to the intakemanifold. As depicted, canister check valve 116 may also be a ball checkvalve, although alternative check valves may be used. In the depictedexample, check valve 116 includes a spring which pre-positions the valvein a closed configuration. As such, the spring may be optional as theflow of air and vapors, depending on the forward or reverse flow, maydrive the check valve to the requisite configuration. Thus, duringforward flow, check valve 116 may permit the unidirectional flow of airfrom canister 202 to intake manifold 44. In the event of high pressureair entering the purge line from intake manifold 44, canister checkvalve 116 may close, thereby preventing the pressure in fuel tank 20 andcanister 202 from exceeding design limits. However, if canister checkvalve 116 is stuck open, high pressure air may enter the fuel vaporrecovery system from a boosted intake manifold 44. While the depictedexample shows the canister check valve positioned between the canisterpurge valve and the intake manifold, in alternate embodiments, the checkvalve may be positioned before the purge valve.

Fuel tank pressure transducer (FTPT) 120, or fuel tank pressure sensor,may be included in purge line 28, coupled between the fuel tank and theengine intake or along vent 27, coupled between the fuel vapor canisterand the canister vent valve. As such, FTPT 120 may be configured toidentify leaks in the fuel vapor recovery system 22. Engine-off naturalvacuum (EONV) leak detection may be enabled by observing changes in apressure value of the FTPT (for example, failure to hold a vacuum).Specifically, during leak detection, an engine controller may beconfigured to monitor the presence of a vacuum in the sealed fuel tankafter engine shut-off by monitoring the pressure change across afuel-tank mounted FTPT. A drop in pressure, or vacuum, may occur as thefuel cools down over several minutes following engine shut-off. If avacuum can be drawn, the system has no leaks. In contrast, if a vacuumcannot be drawn, a leak may be present.

It will be appreciated that current EONV detection methods utilize aFTPT mounted on the fuel tank or positioned between the fuel tank andthe fuel vapor canister, specifically between fuel tank 20 and tankisolation valve 205. However, herein, the inventors have recognized thatthe FTPT may alternatively be positioned between the fuel canister andthe canister purge valve, and by including a small orifice 222, the FTPTmay be further used as a flow sensor without affecting its ability toperform EONV leak detection. As such, for use as a flow sensor, FTPT 120may be positioned upstream of orifice 222 (as depicted) or alternativelydownstream of orifice 222. Further, orifice 222 may be positionedupstream of the canister purge valve 112. Thus, for flow diagnostics,FTPT 120 and optional downstream orifice 222 may be positioned either inpurge line 28 or in conduit 31, substantially between the fuel tank andthe tank isolation valve. Further still, FTPT 120 and downstream orifice222 may alternatively be positioned in vent 27, with FTPT 120 positionedupstream (or downstream) of orifice 222, and orifice 222 positionedupstream of canister vent valve 108, to enable EONV leak detection andpurge flow diagnostics.

As further elaborated with respect to the routines described in FIGS.7-12, FTPT 120 may be further used as a flow sensor to identify improperflow (such as reverse flow) through the fuel vapor recovery system andto identify component (such as canister purge valve or canister checkvalve) degradation, or as a pressure sensor to identify changes inpressure caused by reverse flow, or combinations thereof. Herein, a fuelvapor recovery system pressure may be estimated by the FTPT and amanifold pressure may be estimated by MAP sensor 218. Subsequently,changes in fuel vapor system pressure, as sensed by FTPT 120, and/orchanges in MAP, as sensed by MAP sensor 218, may be used as a purge gasflow sensor to diagnose improper flow through the fuel vapor recoverysystem (for example, due to a canister purge valve being forced open ora canister check valve stuck open due to valve failure during a boostedengine operation). These changes in pressure may include, for example, acontinued FTPT and/or MAP pressure in a high and maximal operatingrange, or, for example, sudden spikes in FTPT pressure in response to anintermittent closure of the canister vent valve, as further elaboratedherein with reference to the routines of FIGS. 7-12.

The fuel vapor recovery system 22 may be operated by controller 12 in aplurality of modes by selective adjustment of the various valves andsolenoids. For example, the following operating modes may be performed:

Mode A: Fuel Vapor Storage

During select engine and/or vehicle operating conditions, such as duringa fuel tank filling operation and with the engine not running, thecontroller 12 may adjust the duty cycle of an associated solenoid andintermittently open the canister vent valve to direct fuel vaporsthrough conduit 31, and into fuel vapor canister 202. Additionally inthis mode, the controller may close canister purge valve 112 (byadjusting the duty cycle of canister purge valve solenoid 214) toprevent fuel vapors from being purged into the intake manifold. As such,under these conditions, canister check valve 116 may remain open orclosed.

Mode B: Fuel Vapor Canister Purging

During select engine and/or vehicle operating conditions, such as afteran emission control device light-off temperature has been attained andwith the engine running, the controller 12 may adjust the duty cycle ofthe canister vent valve solenoid and open canister vent valve 108. Atthe same time, controller 12 may adjust the duty cycle of the canisterpurge valve solenoid 214 and open canister purge valve 112. In this way,the vacuum generated by the intake manifold of the operating engine maybe used to draw fresh air through vent 27 and through fuel vaporcanister 202 to purge the stored fuel vapors into intake manifold 44. Inthis mode, the purged fuel vapors from the canister are combusted in theengine.

In yet another embodiment, rather than using fresh air that is atatmospheric pressure, compressed or boosted air, that is air that hasbeen passed through a compressor of a boosting device (such as aturbocharger or a supercharger) may be used for a boosted purgingoperation. As such, fuel vapor recovery system may require additionalconduits and valves for enabling a boosted purging operation. In stillanother embodiment, a short-circuited compressor flow can be configuredto produce a vacuum to draw in purge air, as further elaborated in FIG.6.

During purging, the learned vapor amount/concentration can be used todetermine the amount of fuel vapors stored in the canister, and then,during a later portion of the purging operation (when the canister issufficiently purged or empty), the learned vapor amount/concentrationcan be used to estimate a loading state of the fuel vapor canister.

FIG. 3 shows another example embodiment 300 of fuel vapor recoverysystem 22. In the depicted embodiment, FTPT 120 is positioned betweenfuel vapor canister 202 and canister check valve 116, but along branchedpurge line 428, substantially parallel to purge line 28, andsubstantially across canister purge valve 112. Small orifice 222 mayalso be included in branched purge line 428. By measuring pressurechanges across the small orifice, FTPT 120 may be able to identifyreverse flow in the purge line, without affecting its original role inEONV leak detection. In this way, the FTPT may be used as a flow meter,detecting a direction and amount of flow of purged fuel vapors whenpurge flow is in the forward direction (that is, from the fuel vaporcanister 202 to the intake manifold 44), and a direction and amount ofboosted air from a boosted intake manifold when flow is in the reversedirection (that is, from the intake manifold to the canister).

FIG. 4 depicts example embodiment 400 of fuel vapor recovery system 22.As such, embodiment 400 may be substantially similar to the embodimentpreviously introduced in FIGS. 2-3. However, herein check valve 116 maybe omitted. While the depicted example shows FTPT 120 coupled to orifice222, in an alternate embodiment, FTPT 120 may not be coupled to orifice222, but may be coupled to the throat of a venturi, as elaborated belowwith reference to FIG. 5, for flow diagnostics. Additionally, due to thelack of check valve 116, diagnostic routines monitoring flow through thefuel vapor recovery system (such as the routine of FIG. 11) may beconfigured to assess canister purge valve degradation related reverseflow issues.

FIG. 5 shows an alternate embodiment 500 of fuel vapor recovery system22. In the depicted embodiment, FTPT 120 is coupled to the throat of aventuri 522. By coupling the FTPT to the venturi, the flow sensitivityof the FTPT may be enhanced. Specifically, the coupled configuration mayenable the FTPT to maintain its original function in EONV leakdetection, while further enabling the FTPT to be used as a flow sensor.While the depicted embodiment shows the venturi (with the coupled FTPT)positioned between the intake manifold 44 and the fuel vapor canister202, in an alternate embodiment, the venturi (with the coupled FTPT) maybe positioned between the canister and the atmosphere, along vent 27. Inthe venturi-coupled configuration, the FTPT output may aid enginecontroller 12 to diagnose and indicate a reverse flow through the systembased on a pressure difference estimated by the FTPT before and aftersealing the fuel vapor system at least from the engine intake. As such,a venturi-based flow sensor may not be able to detect a flow direction.However, under boosted conditions, that is, when MAP (as determined byMAP sensor 218) is greater than the barometric pressure (BP), thepresence of any flow across the venturi may be ascribed to flow in areverse direction. In contrast, if MAP is lower than BP, the presence ofany flow (or a lack of flow) across the venturi may be correlated withan absence of reverse flow through the fuel vapor recovery system.Specifically, (as further elaborated with reference to FIG. 12) in theevent of no flow across the venturi, for example during an engine-offnatural vacuum, the FTPT may detect a static pressure. In contrast, inthe case of a reverse flow during boosted engine operation, the FTPT maydetect a pressure drop. Since venturis have an inherent pressurerecovery mechanism, a lower pressure drop may be obtained with venturi322 versus the pressure restriction of orifice 222 of FIG. 2.

FIG. 17 shows another embodiment 1700 of fuel vapor recovery system 22.As such, embodiment 1700 may be substantially similar to the embodimentpreviously introduced in FIG. 5. However, herein FTPT 120 may bepositioned along conduit 31, substantially between tank isolation valve205 and fuel tank 20. Furthermore, FTPT 120 may neither be coupled to anorifice nor a venturi.

Now turning to FIG. 6, a double path purge system for fuel vaporrecovery system 22 is elaborated. Specifically, such a double path purgesystem allows the fuel vapors in the fuel vapor canister to be purgedinto the intake manifold either directly using an intake manifoldvacuum, or alternatively, with a boost system created vacuum.

FIG. 6 depicts example embodiment 600 of fuel vapor recovery system 22wherein the fuel vapors may be purged with boosted intake air. Herein,canister purge valve 112 and canister check valve 116 may regulate flowof vapors and air between fuel vapor canister 202 and the intakemanifold 44 along purge line 28 that may be further split into purgelines 628 a and 628 b. As previously depicted in FIG. 3, FTPT 120 ispositioned between fuel vapor canister 202 and canister purge valve 112,with FTPT 120 being connected to the throat of venturi 322. However, inalternate embodiments, FTPT 120 may not be connected to a venturi, andinstead a small orifice 222 may be provided (for example, as inembodiment 200 of FIG. 2) to enable EONV leak detection and flowdiagnostics. Further still, in alternate embodiments, FTPT 120 connectedto the throat of venturi 522 may be located in vent 27.

In the depicted embodiment, fuel vapors may be purged along two paths,as indicated by split purge lines 628 a and 628 b. When purging fuelvapors directly into intake manifold 44, using an intake manifoldvacuum, fuel vapors may proceed along purge line 628 a (dashed arrow).Alternatively, fuel vapors may be purged using a boost system createdvacuum. As depicted, exhaust gas flow through exhaust manifold 25 maydrive a turbine 75 connected to the compressor 74 of a boosting device,such as a turbocharger or a supercharger, via shaft 76. Compressor 74may be configured to provide a boost to intake air received along intakepassage 642. While part of the boosted intake air may be provideddirectly to the intake manifold 44, the other part may be circulatedalong conduit 630 towards venturi 622. Flow of boosted air throughventuri 622 may then create a venturi effect that may enable purge flowfrom purge line 628 b to also be drawn in to venturi 622. In this way, aboosted purge flow may be generated along conduit 632, which may then bepurged to the intake manifold. An additional check valve 616 may beincluded in purge line 628 b to ensure unidirectional flow of vaporsalong purge line 628 b. As such, during a boosted purging operation,canister check valve 116 may remain closed while check valve 616 may beopened. In the event of a degradation of check valve 116 (that is, checkvalve 116 remains stuck open), the boosted purging mixture may causecanister purge valve 112 to be forced open and reverse flow may ensue.By using FTPT 120 as a flow meter, and further using diagnostic routinessuch as those depicted in FIGS. 7-12 and 15-16, such improper flows maybe rapidly detected and appropriate measures (such as an immediatedisabling of the boost) may be taken in a timely manner.

In this way, as illustrated in FIGS. 2-6 and 17, an FTPT may diagnoseimproper flow through a vapor recovery system (either via flowinference, or pressure readings) in addition to its function in EONVleak detection. While the depicted embodiments use an FTPT, it will beappreciated that in alternate embodiments, a flow meter may be usedalternatively or additionally. By using the FTPT, the need foradditional hardware components (such as an additional pressure sensorand pressure relief valves) for flow diagnostics may be reduced, therebyreducing the number of components required for flow diagnostics(although additional sensors may be used, if desired). By identifyingimproper flow through the vapor recovery system at an early stage,component damage, as may be caused by improper and over-pressurized airflow through the system components, may be reduced. Additionally,over-pressure induced fuel vapor emissions may be reduced.

Controller 12 may be configured to identify flow errors and componentdegradation (such as check valve and/or canister purge valvedegradation) using pressure-change based diagnostic routines. In oneexample, the pressure-change based diagnostic routines may includecomparing a first and second pressure value estimated before and aftersealing the fuel vapor recovery system (for example, before and aftersealing the fuel vapor recovery system from the intake manifold and/orthe atmosphere). In another example, the pressure-change baseddiagnostic routines may include comparing a first and second change inpressure estimated before and after sealing the fuel vapor recoverysystem (for example, before and after sealing the fuel vapor recoverysystem from the intake manifold and/or the atmosphere). By performingpressure-based diagnostic routines, the controller may identify thepresence or absence of reverse flow, and further identify componentdegradation that may be responsible for the reverse flow. By furthercommanding mitigating measures, for example boost disablement,responsive to the detection of a reverse flow, further degradation ofthe fuel vapor recovery system may be reduced. It will be appreciatedthat while the diagnostic routines depicted in FIGS. 7-12, and 15-16disable boost responsive to an indication of degradation, in alternateembodiments, additional or alternate mitigating measures may be used.

In one particular approach, during boosting, the canister purging systemcan be monitored to identify reverse flow from the intake manifold into(and through) the canister purging system. In such conditions, the flowthrough the canister purging system will generate pressure in thecanister purging system that can be monitored. Additionally, oralternatively, the flow itself can be monitored. The conditions underwhich such reverse flow can occur can be caused to occur, or may occurnaturally during vehicle operation.

Also, parameters of the canister purging system can be adjusted toenhance the detectability of such reverse flow conditions. For example,restriction in the canister purging system can be enhanced so that anyreverse flow that inadvertently occurs will cause a greater impact onobserved pressure. For example, increasing a restriction out of thecanister purging system (e.g., by closing a canister vent valve) under acondition in which reserve flow is present (e.g., due to a degradedcheck valve or purge valve) generates a more rapid and greater pressurerise in the canister purging system.

Finally, active adjustment of parameters of the canister purging systemmay be used to increase correlation of sensed data to degradationconditions. As such, if an amount of reverse flow is affected byadjusting a restriction of the canister purging system (e.g., byadjusting a canister vent valve), then it may be possible to monitorpressure in the canister purging system and correlate changes of thatpressure with the commanded changes aimed at adjusting the systemrestriction. In one example, if the pressure in the canister purgingsystem changes in concert with changes in the vent valve under acondition in which the intake manifold is commanded to be sealed fromthe canister purging system, then this indicates that in actuality thecommanded seal has not been sufficiently achieved. In another example,if the pressure in the canister purging system does not change inconcert with changes in the purge valve (where the intake manifold iscommanded to be sequentially sealed and unsealed from the canisterpurging system), this can indicate that in both cases the seal was notpresent, or in both cases it was present—neither of which includesproper functioning. Moreover, rather than, or in addition to, monitoringpressure of the pressure in the canister purging system changes inconcert with changes in the vent valve under a condition in which theintake manifold is commanded to be sealed from the canister purgingsystem, changes (or lack thereof) in manifold pressure may be used.

FIGS. 7-12 depict example diagnostic routines that may be performed bycontroller to monitor reverse flow of fuel vapors and/or air through avehicle fuel vapor recovery system. The different routines enabledegradation to be indicated, during boost, based on a pressure value inthe system, when the fuel vapor recovery system is commanded to besealed, partially un-sealed, or intermittently sealed, from the engineintake and/or atmosphere. Similarly, FIGS. 15-16 depict examplediagnostic routines that may be performed by controller to monitorreverse flow of fuel vapors and/or air through a vehicle fuel vaporrecovery system, during boost, based on the presence of a flow throughthe system, when the fuel vapor recovery system is commanded to besealed, partially un-sealed, or intermittently sealed, from the engineintake and/or atmosphere. FIG. 7 depicts a diagnostic routine 700 foridentifying improper flow through the fuel vapor recovery system.Specifically, the routine may identify reverse flow of air through thecanister purging system, for example due to entry of boosted air intothe canister from the intake manifold due to a canister purge valve thatis stuck open or due to a degraded canister check valve. As such,diagnostic routine 700 may be used in an embodiment of the fuel vaporrecovery system including, or not including, a canister check valve,(one example of which is illustrated in the embodiments of fuel vaporrecovery system 22 including FTPT 120 coupled upstream of orifice 222).By diagnosing reverse flow and then disabling boost in response to thediagnosis, improper flow of higher pressure air from the intake manifoldto the canister and fuel tank may be reduced, thereby reducing the riskof the canister and/or fuel tank from exceeding design limits ofpressure, while also reducing undesirably high fuel vapor emissions intothe atmosphere.

At 702, it is determined whether a purge diagnostics mode has beenenabled or not. That is, it determined whether the settings on thecontroller have been set for purge diagnostics. In one example, this mayinclude adjusting duty cycles for the solenoids associated with thecanister vent valve and/or the canister purge valve. If purgediagnostics have not been enabled at 702, then at 704, it is enabled.Next at 706, the settings for the diagnostic routine may be commanded.This may include commanding the canister purge valve (CPV) to be closed,open, or partially open, by accordingly adjusting the state of thecanister purge valve solenoid. For example, in systems including a checkvalve in series with the CPV (e.g., FIG. 2), the CPV may be commandedopen to diagnose the check valve. Alternatively, in systems without acheck valve in series with the CPV, the CPV may be commanded closed. Inone example, by commanding the canister purge valve to be closed, thefuel vapor recovery system may be sealed from the engine intake.

The commanding of diagnostic settings may further include commanding thecanister vent valve to be closed, by accordingly adjusting the state ofthe canister vent solenoid. By commanding the canister vent valve (CVV)to be closed, the fuel vapor recovery system may be sealed from theatmosphere. However, in alternate embodiments, the canister vent valvemay remain open. As such, since the diagnostic routine is based on apressure measurement of the FTPT, by commanding the canister vent valveto be closed, a relatively larger pressure difference may be observed ina shorter diagnostic interval. Commanding the settings for thediagnostic routine may further include commanding an optional tankisolation valve (TIV) of the fuel vapor recovery system to be closed.However, in alternate embodiments, the tank isolation valve may remainopen. Since the diagnostic routine is based on a pressure measurement ofthe FTPT, by commanding the tank isolation valve to be closed, during areverse flow, the detectable pressure difference may be observedrelatively faster, for example within a few seconds of sealing thesystem. Additionally, by concurrently closing the tank isolation valvealong with the canister vent valve, the risk of inflating the liquids inthe fuel tank may be reduced.

At 708, the manifold absolute pressure (MAP) and barometric pressure(BP) may be measured and/or estimated. At 710, it may be determinedwhether the MAP is greater than the BP, that is, if a boosted conditionis present. If no boost is present, then the diagnostic routine may end.However, if a boosted condition is established, at 712, a pressure valuein the fuel vapor recovery system may be estimated by the FTPT and thepressure value (P_(FTPT)) may be noted. At 714, it may be determinedwhether, under the given diagnostic settings (for example, with the fuelvapor recovery system sealed from the intake), if the pressure value(P_(FTPT)) is greater than a threshold. In one example, it may bedetermined whether the absolute pressure of the system, as estimated bythe FTPT, has risen above a threshold. In another example, the rate ofpressure change, for example, the rate of pressure rise, may beestimated. In yet another example, a pressure difference, for example, apressure difference between the boost pressure and the system pressure(P_(FTPT)) may be compared to a threshold value. The boost pressure maybe calculated as a difference between the estimated manifold airpressure and the barometric pressure, that is, as (MAP−BP). The pressuredifference between the boost pressure and the fuel vapor recovery systempressure may then be calculated as {(MAP−BP)−P_(FTPT)}. In still anotherexample, a pressure difference between a first pressure estimated beforesealing the system and a second pressure estimated after sealing thesystem may be compared to the threshold. Further still, other pressuredifference calculations may also be used. As such, the threshold may bean absolute pressure value or a pressure range. Furthermore, thethreshold may be adjusted responsive to the boost pressure. Thus, as theboost pressure increases, the threshold may be increased.

In one example, the threshold may be a maximal in-range pressure of theFTPT. If under the diagnostic routine conditions (for example, with theCPV, CVV, and TIV closed), the pressure value (for example, the absolutepressure P_(FTPT), or the calculated pressure difference) is not abovethe threshold, then a normal flow of air and vapors through the fuelvapor recovery system may be deduced at 716. If the pressure value isgreater than the threshold, for example, if P_(FTPT) is consistently inthe maximal pressure range of the sensor, then an improper or reverseflow of air and vapors through, and degradation of, the fuel vaporrecovery system may be concluded at 718. Accordingly, a diagnostic codemay be set at 720 to indicate degradation and reverse flow through thesystem. Additionally, to reduce the chance that the boosted air flowsimproperly into the fuel vapor canister and fuel tank, boost may bedisabled (for example, by disabling the boosting device) at 722, inresponse to the indication of degradation. In this way, degradation ofthe fuel vapor recovery system may be diagnosed during boost, inresponse to a pressure value in the system being greater than athreshold, and further, may be promptly addressed.

In FIGS. 8-9, diagnostic routines are described wherein byintermittently adjusting a restriction in the fuel vapor recovery systemduring boosted conditions, reverse flow and degradation of a fuel vaporrecovery system may be indicated based on a change in pressure value inthe system. Herein, the pressure value may include a fuel vapor recoverysystem pressure, as estimated by FTPT 120, an engine intake manifoldpressure, as estimated by MAP sensor 218, or a pressure differencebetween a first pressure estimated before adjusting the restriction anda second pressure value estimated after adjusting the restriction.

Now turning to FIG. 8, another diagnostic routine 400 is described foridentifying improper flow, such as reverse flow, through the fuel vaporrecovery system. As such, in the routine of FIG. 7, a gradual change ina pressure value is used to determine reverse flow in the system. Incontrast, the routine of FIG. 8 determines reverse flow through thesystem based on more sudden changes (for example, sudden spikes) inpressure value estimated by the FTPT in response to an intermittentclosing of the canister vent valve. Diagnostic routine 800 may be usedin an embodiment of the fuel vapor recovery system including, or notincluding, a canister check valve, as illustrated in the embodiments offuel vapor recovery system 22 including FTPT 120 coupled upstream oforifice 222.

At 802, it is determined whether a purge diagnostics mode has beenenabled or not. If purge diagnostics have not been enabled at 802, thenat 804, it is enabled. Next, at 806, it is determined whether thecanister purge valve has been commanded to be closed. If the canisterpurge valve (CPV) is not closed at 806, then at 808, the CPV is closed.At 810, MAP and BP may be measured and/or estimated. At 812, it may bedetermined whether MAP is greater than BP, that is, if a boostedcondition is present. If no boost is present, then the diagnosticroutine may end. Once a boosted condition has been established, at 816,the FTPT may be read and the pressure value (P_(FTPT)) may be noted. At818, the canister vent valve may be commanded to be closed.Additionally, along with the canister vent valve, the tank isolationvalve may also be closed. However, in alternate embodiments, the(optional) tank isolation valve may remain open. As previouslyexplained, by closing the tank isolation valve, the diagnostics time maybe reduced by enabling a faster detection of a pressure change. Sincethe diagnostic routine is based on a pressure measurement of the FTPT,in the event of a reverse flow, a sudden change in pressure, for examplea sudden spike or increase in pressure, may be expected at the time ofcanister vent valve closing. Accordingly, at 820, it may be determinedwhether P_(FTPT) suddenly exceeds a threshold. As such, the thresholdmay be an absolute pressure value or a pressure range. If in response tocanister vent valve closure, P_(FTPT) does not spike, then a normal flowof air and vapors through the fuel vapor recovery system may beconcluded at 822. In contrast, if P_(FTPT) spikes in response to thesudden canister vent valve closure, and the pressure is greater than thethreshold, then an improper or reverse flow of air and vapors throughthe fuel vapor recovery system may be concluded at 824. While thedepicted example uses an absolute value of P_(FTPT) to diagnose reverseflow, as previously elaborated, it will be appreciated that in alternateembodiments, a rate of pressure change or a pressure difference, or analternate pressure value may be used to diagnose the reverse flow.

In response to a determination of reverse flow at 824, a diagnostic codemay be set at 826. Additionally, to reduce the chance that the boostedair flows into the fuel vapor canister and fuel tank, boost may bedisabled at 828. In one example, the diagnostic routine of FIG. 8 may berun with a predetermined periodicity (for example, once every drivecycle if a boosted condition is reached for a length of time that wouldenable flow detection) such that the canister vent valve isintermittently closed and the consequent change in P_(FTPT) is monitoredover time. In the event of an improper flow, P_(FTPT) may be expected torise and fall with a periodicity matching the (intermittent) opening andclosing of the canister vent valve.

Now turning to FIG. 9, another diagnostic routine 900 is described foridentifying improper flow, such as reverse flow, through the fuel vaporrecovery system. In contrast to the routine of FIG. 8, the routine ofFIG. 9 determines reverse flow through the system based on pressurechanges related to intake manifold pressure, as estimated by the MAPsensor, in response to an intermittent closing of the canister ventvalve. Diagnostic routine 900 may be used in an embodiment of the fuelvapor recovery system including, or not including, a canister checkvalve, as illustrated in the embodiments of fuel vapor recovery system22 including FTPT 120 coupled upstream of orifice 222.

At 902, it is determined whether a purge diagnostics mode has beenenabled or not. If purge diagnostics have not been enabled at 902, thenat 904, it is enabled. Next, at 906, it is determined whether thecanister purge valve has been commanded to be closed. If the canisterpurge valve is not closed at 906, then at 908, the purge valve isclosed. At 910, MAP and BP may be measured and/or estimated. At 912, itmay be determined whether MAP is greater than BP, that is, if a boostedcondition is present. If no boost is present, then the diagnosticroutine may end. Once a boosted condition has been established, at 914,the canister vent valve may be closed. Additionally, along with thecanister vent valve, the tank isolation valve may also be closed toexpedite the pressure change and the diagnostic routine. However, inalternate embodiments, the tank isolation valve may remain open. Assuch, closing of the canister vent valve causes flow out of the canisterto be blocked and may further cause any improper flow out of the intakemanifold to also be blocked. Consequently, in the case of improper flowthrough the system, MAP may be expected to rise in response to canistervent valve closure. Accordingly, at 916, it may be determined whetherMAP suddenly spikes and exceeds a predetermined threshold. As such, thethreshold may be an absolute pressure value or a pressure range. If inresponse to canister vent valve closure, MAP does not spike, then anormal flow of air and vapors through the fuel vapor recovery system maybe concluded at 918. In contrast, if MAP spikes in response to canistervent valve closure, and the pressure is greater than the threshold, thenan improper or reverse flow of air and vapors through the fuel vaporrecovery system may be concluded at 920. Additionally, a diagnostic codemay be set at 922 to indicate reverse flow through the system. Further,boost may be disabled at 924.

In one example, the diagnostic routine of FIG. 9 may be run with apredetermined periodicity (for example, once every drive cycle if aboosted condition is reached for a length of time that would enable flowdetection) such that the canister vent valve is occasionally closed andthe consequent change in MAP is monitored. In the event of an improperflow, MAP may be expected to rise and fall with a periodicity matchingthe opening and closing of the canister vent valve. An example of such amap is provided herein with reference to FIG. 13.

While in the depicted examples of FIGS. 8-9, intermittently adjustingthe restriction includes intermittently sealing the fuel vapor recoverysystem from the atmosphere by intermittently commanding the canistervent valve to be closed, in alternate embodiments, the restriction maybe intermittently adjusted by intermittently sealing the fuel vaporrecovery system from the intake by intermittently commanding thecanister purge valve to be closed. Additionally, while the depictedexamples illustrate indicating degradation based on a change in apressure value, in alternate embodiments, indicating degradation may bebased on a change in flow in the system. In one example, FTPT 120 may becoupled to a venturi and the change in flow may be estimated by thepresence of a flow across the venturi (for example, based on a pressuredifference across the venturi being greater than a threshold). Furtherstill, while the depicted example correlates system degradation withreverse flow, in alternate embodiments, the routine may furthercorrelate reverse flow and system degradation to a componentdegradation, for example, degradation of a check valve.

In FIG. 13, map 1300 depicts a state of the canister vent valve (CVV) at1302. Herein, the CVV may be periodically shifted between open andclosed states. At 1304, a corresponding change in manifold pressure(MAP) is depicted. As illustrated, between time points t₁ and t₂, inresponse to CVV closure, no substantial change in MAP may be observed.Thus, a normal flow of vapors through the fuel vapor recovery system maybe concluded during this time frame. In contrast, between time points t₃and t₄, in response to CVV closure, a rise in MAP may be observed, theMAP subsequently falling in response to CVV opening. Herein, an improperor reverse flow of vapors through the fuel vapor recovery system may beconcluded during this time frame. In this way, using a map, such as map1300, the diagnostic routine of FIG. 9 may be configured to detectimproper flow of vapors through the fuel vapor recovery system.

Now turning to FIG. 10, an example diagnostic routine 1000 foridentifying reverse flow due to degradation in a canister check valve,coupled in series with the canister purge valve, is described. Byidentifying degradation in the canister check valve, for exampleidentifying that the check valve is stuck open when it should be closed,reverse air flow (from the intake manifold to the canister and fueltank) detection may be expedited. In the case of canister check valvedegradation during a boosted engine operation, improper flow of higherpressure air from the intake manifold can cause the canister and fueltank to exceed design limits of pressure, while also causing undesirablyhigh fuel vapor emissions into the atmosphere. As such, diagnosticroutine 1000 may be used in embodiments of the fuel vapor recoverysystem wherein a canister check valve is included.

At 1002, it is determined whether a purge diagnostics mode has beenenabled or not. If purge diagnostics have not been enabled at 1002, thenat 1004, it is enabled. At 1006, MAP and BP may be measured and/orestimated. At 1008, it may be determined whether the MAP is greater thanthe BP, that is, if a boosted condition is present. As such, thedifference between the estimated MAP and the estimated BP may representa boost pressure. If no boost is present, then the routine may end. Oncea boosted condition has been established, at 1010, the settings for thediagnostic routine may be commanded. This may include commanding thecanister vent valve (CVV) to be closed, by accordingly adjusting thestate of the canister vent solenoid. By commanding the canister ventvalve to be closed, the fuel vapor recovery system may be sealed fromthe atmosphere. However, in alternate embodiments, CVV may remain open.Additionally, the fuel vapor recovery system may be at least partiallyun-sealed from the engine intake during the boosted condition. Herein,the canister purge valve (CPV) may be commanded to be opened, or atleast partially opened, by accordingly adjusting the state of thecanister purge valve solenoid. Degradation may then be indicated basedon a pressure transducer positioned between the fuel vapor canister andthe engine intake. In one example, during an “active diagnostics” mode,the CPV may be actively commanded to be opened, under boosted engineconditions, to verify check valve operation. In doing so, the controllermay actively ensure that under conditions of boost, and even underconditions of a degraded CPV (that is, an open CPV), the check valve isoperational and is able to prevent boosted air flow from entering thefuel vapor recovery system. Further still, the tank isolation valve(TIV) of the fuel vapor recovery system may be commanded to be closed.However, in alternate embodiments, the tank isolation valve may remainopen. Since the diagnostic routine is based on a pressure measurement ofthe FTPT, by commanding the tank isolation valve and the canister ventvalve to be closed, during a reverse flow, the detectable pressuredifference may be observed relatively faster, for example within a fewseconds of sealing the system. Additionally, by concurrently closing thetank isolation valve along with the canister vent valve, the risk ofinflating the liquids in the fuel tank may be reduced.

At 1012, the fuel vapor recovery system pressure, as indicated by theFTPT pressure value (P_(FTPT)), may be read. In one example, as furtherelaborated in FIG. 14, the pressure may be monitored for a predeterminedtime, for example, a test time. A timer may be started when the canistervent valve is closed to mark a starting time of P_(FTPT) monitoring. Thecanister vent valve may then be opened once the time on the timer haselapsed. At 1014, it may be determined whether the estimated pressure isgreater than a threshold. As such, the threshold may be an absolutepressure value or a pressure range. Furthermore, the threshold may beadjusted responsive to the boost pressure. If the estimated pressuredifference is not above the threshold, then at 1016, normal canistercheck valve operation and a proper flow of air and/or vapors through thefuel vapor recovery system may be concluded. In one example, if theestimated pressure is greater than the threshold, then at 1018, it maybe concluded that the canister check valve has degraded, for example, itmay be determined that the check valve is stuck open and that a reverseflow of air and/or vapors through the fuel vapor recovery system inunder way. In another example, as elaborated in FIG. 14, it may bedetermined whether the estimated pressure exceeded the pressurethreshold for an amount of time greater than a predetermined fault timethreshold. Accordingly a diagnostic code may be set at 1020 to indicatethe canister check valve degradation. Additionally, boost may bedisabled at 1022. While the depicted example uses an absolute value ofP_(FTPT) to diagnose canister check valve degradation, as previouslyelaborated, it will be appreciated that in alternate embodiments, a rateof pressure change or a pressure difference, or an alternate pressurevalue may be used to diagnose the reverse flow.

To further explain the routine of FIG. 10, an example map is providedherein with reference to FIG. 14. In FIG. 14, map 1400 depicts a stateof the canister vent valve (CVV) at 1402. Herein, the CVV may be openedfor a predetermined test time, as illustrated at 1410. Specifically, att₁, a test timer may be started and CVV may be opened, for example, byenergizing the associated canister vent solenoid. When the test timerexceeds a predetermined test time threshold 1409, or if a check valvefault is identified (such as at t₅), the CVV may be closed, for example,by de-energizing the associated canister vent solenoid. Curve 1404represents the output of the FTPT, P_(FTPT), over the period of the testtime. A fault timer may be configured to count a cumulative fault time,as indicated at 1406, in response to P_(FTPT) rising above a pressurethreshold 1403. Thus, as illustrated, between test time t₂ and t₃, andagain between t₄ and t₅, in response to P_(FTPT) being greater thanpressure threshold 1403, a cumulative fault time on the fault timer maybe incremented. As such, between t₃ and t₄, when P_(FTPT) is below thepressure threshold, the fault timer is not incremented. At t₅, inresponse to the cumulative fault time exceeding a fault time threshold1405, a check valve fault may be concluded and indicated at 1408.Furthermore, to prevent further pressure build-up in the fuel vaporrecovery system, the canister vent valve may be closed at t₅. In thedepicted example, the diagnostic routine enables a check valvedegradation to be identified before the end of the test time. In thisway, using a map such as the map of FIG. 14, the diagnostic routine ofFIG. 10 may be configured to identify canister check valve degradationand related improper flow of vapors through the fuel vapor recoverysystem, and address the degradation in an expedited manner.

Now turning to FIG. 11, an example diagnostic routine 1100 foridentifying reverse flow due to degradation in a canister purge valve isdescribed. As such, diagnostic routine 1100 may be advantageously usedin an embodiment of the fuel vapor recovery system wherein a check valveis not included, such as the embodiment of FIG. 4. However, the routinemay also be used in alternate embodiments wherein the canister checkvalve is present. By identifying degradation in the canister purgevalve, for example identifying that the canister purge valve is stuckopen when it should be closed, detection of reverse air flow (from theintake manifold to the canister and fuel tank) may be expedited. In thecase of canister purge valve degradation during a boosted engineoperation, improper flow of higher pressure air from the intake manifoldcan cause the canister and fuel tank to exceed design limits ofpressure, while also causing undesirably high fuel vapor emissions intothe atmosphere.

At 1102, it is determined whether a purge diagnostics mode has beenenabled or not. If purge diagnostics have not been enabled at 1102, thenat 1104, it is enabled. At 1106, MAP and BP may be measured and/orestimated. At 1108, it may be determined whether the MAP is greater thanthe BP, that is, if a boosted condition is present. As such, thedifference between the estimated MAP and the estimated BP may representa boost pressure. If no boost is present, then the routine may end. Oncea boosted condition has been established, at 1110, the settings for thediagnostic routine may be commanded. This may include commanding thecanister vent valve (CVV) to be closed, by accordingly adjusting thestate of the canister vent solenoid. By commanding the canister ventvalve to be closed, the fuel vapor recovery system may be sealed fromthe atmosphere. However, in alternate embodiments, CVV may remain open.Additionally, the canister purge valve may be commanded to be closed, byaccordingly adjusting the state of the canister purge valve solenoid. Bycommanding the canister purge valve to be closed, the fuel vaporrecovery system may be sealed from the intake. Further still, the tankisolation valve (TIV) of the fuel vapor recovery system may be commandedto be closed. However, in alternate embodiments, the tank isolationvalve may remain open. Since the diagnostic routine is based on apressure measurement of the FTPT, by commanding the tank isolation valveand the canister vent valve to be closed, during a reverse flow, thedetectable pressure difference may be observed relatively faster, forexample within a few seconds of sealing the system. Additionally, byconcurrently closing the tank isolation valve along with the canistervent valve, the risk of inflating the liquids in the fuel tank may bereduced.

At 1112, the fuel vapor recovery system pressure, as indicated by theFTPT pressure value (P_(FTPT)), may be read before and after sealing thesystem to the intake. That is, a change in pressure at least before andafter CPV closure may be determined. At 1114, it may be determinedwhether the estimated pressure difference is greater than a threshold.As such, the threshold may be an absolute pressure value or a pressurerange. If the estimated pressure difference is not above the threshold,then at 1116, normal canister purge valve operation and a proper flow ofair and/or vapors through the fuel vapor recovery system may beconcluded. If the estimated pressure difference is greater than thethreshold, then at 1118, it may be concluded that the canister purgevalve has degraded, for example, it may be determined that the purgevalve is stuck open, and that a reverse flow of air and/or vaporsthrough the fuel vapor recovery system in under way. Accordingly adiagnostic code may be set at 1120 to indicate the canister purge valvedegradation. Additionally, boost may be disabled at 1122. While thedepicted example uses a pressure difference to diagnose canister purgevalve degradation, as previously elaborated, it will be appreciated thatin alternate embodiments, a rate of pressure change or an absolutepressure, or an alternate pressure value may be used to diagnose thedegradation.

Now turning to FIG. 12, an example diagnostic routine 1200 is describedfor identifying reverse flow through a fuel vapor recovery system inembodiments of wherein the FTPT is attached to the mouth of a venturi.

At 1202, it is determined whether a purge diagnostics mode has beenenabled or not. If purge diagnostics have not been enabled at 1202, thenat 1204, it is enabled. At 1206, MAP and BP may be measured and/orestimated. At 1208, it may be determined whether the MAP is greater thanthe BP, that is, if a boosted condition is present. If no boost ispresent, then the routine may end. Once a boosted condition has beenestablished, at 1210, the settings for the diagnostic routine may becommanded. This may include commanding the canister purge valve (CPV) tobe closed, by accordingly adjusting the state of the canister purgevalve solenoid. By commanding the canister purge valve to be closed, thefuel vapor recovery system may be sealed from the engine intake. Thismay further include commanding the canister vent valve to be closed, byaccordingly adjusting the state of the canister vent solenoid. Bycommanding the canister vent valve (CVV) to be closed, the fuel vaporrecovery system may be sealed from the atmosphere. However, in alternateembodiments, the canister vent valve may remain open. As such, since thediagnostic routine is based on a pressure measurement of the FTPT, bycommanding the canister vent valve to be closed, a relatively largerpressure difference may be observed. Commanding the settings for thediagnostic routine may further include commanding an optional tankisolation valve (TIV) of the fuel vapor recovery system to be closed.However, in alternate embodiments, the tank isolation valve may remainopen. Since the diagnostic routine is based on a pressure measurement ofthe FTPT, by commanding the tank isolation valve to be closed, during areverse flow, the detectable pressure difference may be observedrelatively faster, for example within a few seconds of sealing thesystem.

At 1212, the fuel vapor recovery system pressure, as indicated by theFTPT pressure value (P_(FTPT)), may be read before and after sealing thefuel vapor recovery system, at least from the engine intake. At 1214, itmay be determined whether the pressure difference between the firstpressure value (P_(FTPT) before sealing the system) and the secondpressure value (P_(FTPT) after sealing the system) is lower than athreshold. As such, the threshold may be an absolute pressure value or apressure range. Furthermore, the threshold may be adjusted responsive tothe boost pressure. If the pressure difference is below the threshold,then it is confirmed that there is a pressure drop across the venturi.As such, during a flow of vapors across a venturi, a significantpressure drop may be expected. While the direction of flow may not beindicated by the venturi, given the prevalent conditions of engineboost, a pressure drop across the venturi may be correlated to reverseflow across the venturi. Thus, if a pressure drop is observed at 1214,at 1218, a reverse flow and degradation of the system may be concluded.Accordingly a diagnostic code may be set at 1220 to indicate theimproper flow. Additionally, boost may be disabled at 1222. If thepressure difference is not below the threshold at 1214, for example, ifthere is no substantial pressure difference and the pressure across theventuri remains static, then at 1216, no reverse flow and degradation ofthe system may be concluded. In an alternate embodiment, the controllermay monitor P_(FTPT) for a predetermined amount of time (as set on atest timer, for example) with the system sealed. If the pressuredifference between a first pressure value recorded at the start of thetimer and a second pressure value recorded at the stopping of the timeris below the threshold, reverse flow may be concluded. In contrast, ifthere is no significant pressure difference and there is an indicationof static pressure for the duration of the timer, no reverse flow may beconcluded. In this way, degradation may be indicated based on thepresence of a flow through the fuel vapor recovery system, during boost,when the system is sealed from the intake.

Now turning to FIG. 15, another example diagnostic routine 1500 foridentifying reverse flow due to degradation in a canister check valve isdescribed. In contrast to the routine of FIG. 10, wherein the pressuresensitivity of the FTPT is used to diagnose check valve degradation, theroutine of FIG. 15 takes advantage of the flow sensitivity of the FTPT.By identifying degradation in the canister check valve, for exampleidentifying that the check valve is stuck open when it should be closed,reverse air flow (from the intake manifold to the canister and fueltank) detection may be expedited. In the case of canister check valvedegradation during a boosted engine operation, improper flow of higherpressure air from the intake manifold can cause the canister and fueltank to exceed design limits of pressure, while also causing undesirablyhigh fuel vapor emissions into the atmosphere. As such, diagnosticroutine 1500 may be used in embodiments of the fuel vapor recoverysystem wherein a canister check valve is included.

At 1502, it is determined whether a purge diagnostics mode has beenenabled or not. If purge diagnostics have not been enabled at 1502, thenat 1504, it is enabled. At 1506, MAP and BP may be measured and/orestimated. At 1508, it may be determined whether the MAP is greater thanthe BP, that is, if a boosted condition is present. As such, thedifference between the estimated MAP and the estimated BP may representa boost pressure. If no boost is present, then the routine may end. Oncea boosted condition has been established, at 1510, the settings for thediagnostic routine may be commanded. This may include commanding thecanister vent valve (CVV) to be opened, by accordingly adjusting thestate of the canister vent solenoid. By commanding the canister ventvalve to be opened, the downstream pressure may be known while theupstream pressure is read by the FTPT. Additionally, the canister purgevalve (CPV) may be commanded to be opened, or partially opened, byaccordingly adjusting the state of the canister purge valve solenoid. Inone example, during an “active diagnostics” mode, the CPV may beactively commanded to be opened, under boosted engine conditions, toverify check valve operation. In doing so, the controller may activelyensure that under conditions of boost, and even under conditions of adegraded CPV (that is, an open CPV), the check valve is operational andis able to prevent boosted air flow from entering the fuel vaporrecovery system. Further still, the tank isolation valve (TIV) of thefuel vapor recovery system may be commanded to be closed. However, inalternate embodiments, the tank isolation valve may remain open.

It will be appreciated that the flow sensitivity of the FTPT may be usedto identify check valve degradation irrespective of whether the FTPT iscoupled upstream of an orifice or coupled to the mouth of a venturi.Furthermore, the FTPT (and orifice or venturi) may be positioned eitherin vent 27 or along purge line 28. In one example, when the FTPT ispositioned in vent 27, at 1512, a pressure upstream of the orifice orventuri, as indicated by the FTPT pressure value (P_(FTPT)), and apressure downstream of the orifice or venturi, as indicated by theatmospheric pressure (BP) may be read. In another example, when the FTPTis positioned in purge line 28, at 1512, a pressure upstream of theorifice or venturi, as indicated by the FTPT pressure value (P_(FTPT)),and a pressure downstream of the orifice or venturi, as indicated by themanifold pressure (MAP) may be read. At 1514, it may be determinedwhether the pressure difference between the upstream estimated pressureand the downstream estimated pressure is greater than a threshold. Assuch, the threshold may be an absolute pressure value or a pressurerange. If the estimated pressure difference is not above the threshold,then at 1516, normal canister check valve operation and no irregularflow of air and/or vapors through the fuel vapor recovery system may beconcluded. If the estimated pressure is greater than the threshold, thenat 1518, it may be concluded that a flow of vapors across the orifice orventuri has occurred, and that the canister check valve has degraded.Accordingly a diagnostic code may be set at 1520 to indicate thecanister check valve degradation. Additionally, boost may be disabled at1522.

Now turning to FIG. 16, a similar flow-sensitive diagnostic routine 1600for identifying reverse flow due to degradation in a canister purgevalve is described. In contrast to the routine of FIG. 11, wherein thepressure sensitivity of the FTPT was used to diagnose check valvedegradation, the routine of FIG. 16 takes advantage of the flowsensitivity of the FTPT. By identifying degradation in the canisterpurge valve, for example identifying that the check purge is stuck openwhen it should be closed, reverse air flow (from the intake manifold tothe canister and fuel tank) detection may be expedited. Diagnosticroutine 1600 may be advantageously used in embodiments of the fuel vaporrecovery system wherein a canister check valve is not included.

At 1602, it is determined whether a purge diagnostics mode has beenenabled or not. If purge diagnostics have not been enabled at 1602, thenat 1604, it is enabled. At 1606, MAP and BP may be measured and/orestimated. At 1608, it may be determined whether the MAP is greater thanthe BP, that is, if a boosted condition is present. As such, thedifference between the estimated MAP and the estimated BP may representa boost pressure. If no boost is present, then the routine may end. Oncea boosted condition has been established, at 1610, the settings for thediagnostic routine may be commanded. This may include commanding thecanister vent valve (CVV) to be opened, by accordingly adjusting thestate of the canister vent solenoid. By commanding the canister ventvalve to be opened, the downstream pressure may be known while theupstream pressure is read by the FTPT. Additionally, the canister purgevalve (CPV) may be commanded to be closed, by accordingly adjusting thestate of the canister purge valve solenoid. Further still, the tankisolation valve (TIV) of the fuel vapor recovery system may be commandedto be closed. However, in alternate embodiments, the tank isolationvalve may remain open.

In one example, when the FTPT is positioned in vent 27, at 1612, apressure upstream of the orifice or venturi, as indicated by the FTPTpressure value (P_(FTPT)), and a pressure downstream of the orifice orventuri, as indicated by the atmospheric pressure (BP) may be read. Inanother example, when the FTPT is positioned in purge line 28, at 1612,a pressure upstream of the orifice or venturi, as indicated by the FTPTpressure value (P_(FTPT)), and a pressure downstream of the orifice orventuri, as indicated by the manifold pressure (MAP) may be read. At1614, it may be determined whether the pressure difference between theupstream estimated pressure and the downstream estimated pressure isgreater than a threshold. As such, the threshold may be an absolutepressure value or a pressure range. If the estimated pressure differenceis not above the threshold, then at 1616, normal canister purge valveoperation and no irregular flow of air and/or vapors through the fuelvapor recovery system may be concluded. If the estimated pressure isgreater than the threshold, then at 1618, it may be concluded that aflow of vapors across the orifice or venturi has occurred, and that thecanister purge valve has degraded. Accordingly a diagnostic code may beset at 1620 to indicate the canister purge valve degradation.Additionally, boost may be disabled at 1622.

It will be appreciated that in alternate embodiments of the diagnosticroutines of FIGS. 7-12, and 15-16, in addition to detecting reverseflow, the controller may be configured to redirect the reverse flowtowards the engine's air intake passage using a pressure relief valve,for example a pressure relief valve configured along a conduit startingsubstantially between the canister purge valve and the check valve anddirecting flow to the engine's intake passage.

In this way, changes in a pressure or changes in pressure differencesacross a fuel vapor recovery system, for example as estimated by a fueltank pressure sensor coupled to the system, can be used to monitor anddiagnose reverse flow through the fuel vapor recovery system, in aboosted engine. Additionally, the characteristic pressure changes may beused to identify component degradation, such as canister purge valveand/or canister check valve degradation. By identifying characteristicpressure changes across the sensor responsive to reverse flowconditions, excessive evaporative emissions caused by such improper airflow may be reduced. By using routines and sensors that do not requireregular calibration (although in some examples, calibration may beused), the robustness of the detection method can be enhanced.Furthermore, by not necessitating calibration, diagnostic pressurethresholds may be hardcoded into the routines, and improper flow can bemore easily detected by the vehicle PCM. By extending use of the fueltank pressure sensor beyond its function in EONV leak detection, as aflow sensor during both forward and reverse flow, the number of hardwarecomponents required for diagnostic purposes may be reduced.Additionally, the flow sensor may be used to diagnose and characterizeflow through a canister purge valve during forward flow in addition topredicting potential over-pressure related issues during a reverse flow.By identifying reverse flow during a fuel vapor purging operation, andby further identifying degradation in a canister purge valve or checkvalve, over-pressure related component damage and the percentage ofevaporative emissions in a boosted engine exhaust may be significantlyreduced.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. Further, one or moreof the various system configurations may be used in combination with oneor more of the described diagnostic routines. The subject matter of thepresent disclosure includes all novel and nonobvious combinations andsubcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The invention claimed is:
 1. A method for a vehicle fuel vapor system coupled to an engine intake, comprising: during boosted conditions, intermittently adjusting a canister vent valve of a canister, a check valve positioned between the engine intake and the canister; and indicating degradation, including reverse flow of gases from the engine intake to the fuel vapor system, based on a change in a pressure value in the fuel vapor system that correlates to the intermittent adjusting.
 2. The method of claim 1 wherein the pressure value includes a pressure difference between a first pressure value estimated before adjusting the vent valve and a second pressure value estimated after adjusting the vent valve.
 3. The method of claim 1 further comprising disabling boost responsive to the indication of degradation, the disabling of boost including disabling operation of a boosting device coupled in the engine intake.
 4. The method of claim 1 wherein intermittently adjusting the vent valve includes intermittently sealing the fuel vapor system from atmosphere by intermittently commanding the vent valve to be closed.
 5. The method of claim 1 wherein the pressure value includes an engine intake manifold pressure.
 6. The method of claim 5 wherein the manifold pressure is estimated by a manifold pressure sensor coupled to the engine intake.
 7. The method of claim 1 wherein the pressure value includes a rate of change of the pressure value.
 8. The method of claim 7 wherein indicating degradation based on the change in pressure value includes indicating degradation when the change in pressure value is greater than a threshold and setting a diagnostic code.
 9. The method of claim 8 further comprising disabling boost responsive to the indication of degradation, the disabling of boost including disabling operation of a boosting device coupled in the engine intake.
 10. The method of claim 1 wherein the pressure value includes a fuel vapor system pressure.
 11. The method of claim 10 wherein the fuel vapor system pressure is estimated by a fuel tank pressure transducer coupled between a fuel tank and the engine intake.
 12. The method of claim 11 wherein the fuel tank pressure transducer is coupled to a venturi.
 13. The method of claim 12, wherein indicating degradation is further based on presence of a flow across the venturi.
 14. The method of claim 13 wherein indicating degradation based on the presence of the flow across the venturi includes indicating degradation based on a pressure difference across the venturi being greater than a threshold.
 15. A system, comprising: an engine comprising an intake; an exhaust emission control device coupled to the engine; a boosting device with a compressor configured to provide a boost to the engine intake; a fuel vapor system coupled to the engine intake, said fuel vapor system including a fuel tank pressure transducer, a fuel vapor canister, a canister purge valve, a check valve and a canister vent valve; and a control system configured to, intermittently adjust a restriction in the fuel vapor system during a boosted condition; and indicate degradation, including reverse flow of gases from the engine intake to the fuel vapor system, based on a change in pressure value in the fuel vapor system that correlates to the intermittent adjusting.
 16. The system of claim 15 wherein intermittently adjusting a restriction includes intermittently sealing the fuel vapor system from atmosphere by intermittently commanding the canister vent valve to be closed.
 17. The system of claim 16 further comprising a tank isolation valve, wherein intermittently adjusting a restriction further includes intermittently commanding the tank isolation valve to be closed.
 18. The system of claim 17 wherein a fuel tank pressure sensor is positioned between the tank isolation valve and a fuel tank.
 19. The system of claim 16 wherein the pressure value includes at least one of a fuel vapor system pressure estimated by the fuel tank pressure transducer, a manifold pressure estimated by a manifold pressure sensor, a rate of change of the pressure value, and a pressure difference between a first pressure value estimated before adjusting the restriction and a second pressure value estimated after adjusting the restriction.
 20. The system of claim 19 wherein indicating degradation based on the change in pressure value includes indicating degradation when the change in pressure value is greater than a threshold, a controller further configured to set a diagnostic code and disable boost responsive to the indication of degradation, the disabling of boost including disabling operation of a boosting device coupled in the engine intake. 